Re: Multiple firewalls from different manufactureres

[Kevin <kkadow () gmail com>]

On Wed, 26 Jan 2005, Shimon Silberschlag wrote:
> In the past, I used to hear the recommendation that an internet facing
> firewall setup should include at least 2 firewalls from different
> manufacturers. 

Going beyond that, layering distinct types of firewall (filter, proxy, IPS, etc)
running on different base operating systems (PIXOS, BSD, etc) further
reduces the likelihood of an attacker possessing "0 day" exploits against
the entire stack.


On Wed, 26 Jan 2005 16:04:28 -0500 (EST), Paul D. Robertson
<paul () compuwar net> wrote:
> I still try to at least get a screening router up front that does have a
> different packet filtering implementation (so I don't generally use green
> firewalls.)  To me, it's a matter of not designing easy to fail
> infrastructure.

At a minimum, a screening router in front of any firewall makes a lot of sense,
and recently I've started to deploy screening routers on the inside to filter
default route outbound traffic.

It could be seen as designing an infrastructure that is easy to DoS, as any
attack causing any one device in the series to fall will cause the whole
path to stop passing traffic.

The infrastructure might fail more easily, but it should always "fail closed".


> With two devices, you have the chance to catch configuration failures, not
> just implementation failures.  If possible, it's nice to have two
> different groups handling each piece in coordination, so that you have to
> have two people co-opted to start punching holes, especially
> admin-installed backdoors.
>
> With commodity pricing on firewalls, it's really a question of "what do
> you have to lose?"

Deploying multiple different types of security device in series adds cost,
complexity, and failure modes.  Managing the infrastructure requires
more staff with more diverse skills, and the coordination required to
"punch holes" will increase the effort and delay when changes are
legitimately required.

That said, I still think layering can be a good idea.


> Today, when attacks are shifting towards using the already open ports on the
> firewall, at the application level, do you think that such a setup is still
> mandatory and/or recommended?

Yes.


> Do you see such setups implemented? Or does most setups include a
> single FW with multiple DMZs, connected directly to the internal network? 

I see a lot of setups where multiple firewalls from different manufacturers
are deployed, in parallel.


Kevin Kadow
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